Within the past 24 months, Mycoplasma fermentans, strain incognitus, has been linked with respiratory, central nervous system (CNS), and renal disease in AIDS patients. However, the incidence, natural history, pathogenic potential, and clinical significance of M. fermentans in AIDS patients is unknown. Furthermore, there have been no published attempts to determine if the occurrence of other mycoplasmas, several of which are proven pathogens, is increased in AIDS patients. Other mycoplasmas known to cause disease in humans include Mycoplasma pneumoniae, Mycoplasma hominis, and Ureaplasma urealyticum. The latter two are associated with urogenital diseases, but are also known opportunists, causing disseminated disease in hypogammaglobulinemic patients, those undergoing immunosuppressive therapy, and in premature infants. M. pneumoniae is a respiratory pathogen in all age groups accounting for up to 20% of all pneumonias and up to 50% in closed populations. There are several reasons that mycoplasmas may have been previously overlooked in AIDS patients. Mycoplasmas are fastidious and demanding in their requirements for special media and most hospital laboratories lack the capabilities to isolate them. Therefore, diagnosis is often based on exclusion or serological reactions. Without a high index of suspicion, they would not be included in a differential diagnosis and serological reactions may not be diagnostic in HIV-infected persons. The specific aims of the present proposal are: (i) To determine the prevalence of mycoplasmal infections, specifically M. fermentans, M. pneumoniae, M. hominis, M. pirum, U. urealyticum, and M. genitalium in patients with various stages of HIV-1 infection compared to age, sex, and risk-matched non-HIV infected controls; and (ii) To determine if disseminated mycoplasmal infection in particular pneumonitis and central nervous system manifestations not due to other causes, occur in AIDS patients.